1. Technical Field of the Invention
The present invention relates to a safety support for a vehicle wheel with a tire, comprising at least one noise attenuator of the Helmholtz resonator type or the quarter-wave resonator type.
2. The Related Arts
Safety supports for vehicle wheels which use a tire are well-known. Document EP 0 796 747 describes an example of such a support. It consists of a circular body suitable for mounting on the rim of a vehicle. The example illustrated in this document is formed primarily of a vulcanised rubber mix, some zones of which are reinforced, for example with metal- or textile-type filaments. Of course, other materials may be used to produce such a support.
Generally, safety supports are mounted on a rim, within a tire, in order to provide a support for the crown of the tire during travel at low pressure, or even at zero pressure, following a puncture, for example. Thus, direct contact between the tire and the rim, which generally causes virtually instantaneous degradation of the tire, is avoided. The supports therefore make it possible to improve the safety of the vehicle by permitting running for a certain time. This time may furthermore be beneficial in finding a site for making repairs.
Furthermore, the effects caused by acoustic resonance of the air contained in a tire are known. For example, the first cavity mode (sometimes referred to as FCM) is a well-known phenomenon, but the attenuation or suppression thereof always causes numerous difficulties. The natural frequency (or resonant frequency) of a tire is a direct function of its circumference: one wavelength thus corresponds to the circumference of the wheel. A larger wheel means a greater wavelength, and therefore a lower natural frequency. By way of example, a wheel of a diameter of 15xe2x80x3 has a natural frequency of around 230 Hz. The acoustic energy due to the resonant frequency is transmitted primarily in a solid manner. This mode of propagation means that the vibrations caused by the air present in the cavity of the tire are transmitted to the wheel, then to the support and transmission elements, finishing in the passenger compartment, where the occupants are subjected to the transmitted noise.
There are certain ways of attempting to overcome this situation. One such way is described in document WO 98/35843. According to this document, quarter-wave resonators are provided in a specially-designed holder, added to the wheel, in particular by mounting the holder on the rim. This device requires the presence of a specific holder. It is therefore an additional piece, which requires material and manufacturing time, hence supplementary costs, on the one hand, and adding an additional mass to the wheel, on the other hand.
According to a variant embodiment described in this same document, the resonators are provided in the rim. However, such a rim has to undergo major modifications in order to incorporate the resonators.
The present invention is directed at overcoming these various disadvantages, in particular suppressing the acoustic resonance due to the presence of air (or other gas) in the tire cavity or at the very least attenuating the amplitude thereof.
The foregoing and other objects of the invention are attained, according to a first aspect of the invention, by providing a vehicle wheel, comprising a rim, a tire defining with the rim a circumferential cavity C, and at least one resonator suitable for attenuating the amplitude or suppressing a natural resonance of the cavity. The wheel also comprises a safety support, for supporting the tread of the tire from the inside in the event of loss of inflation pressure, which support comprises at least one of the walls of the resonator.
This arrangement, in which the support forms at least one of the walls of a resonator, permits the attenuation of the amplitude, or even the suppression, of one or more natural resonances of the cavity, in particular of the first cavity mode. Each resonator, which is placed so as to communicate with the cavity C, tuned to the frequency or the range of frequencies on which it is desired to act, permits dissipation of the vibrational energy. It is thus possible to minimize or eliminate the transfer of vibration or sound to the passenger compartment via the wheel.
Advantageously, each resonator is formed of a cavity c, occupying a volume V in fluidic communication with the cavity C. Such fluidic communication is advantageously provided by at least one opening.
According to an advantageous variant, the resonator is arranged in the support. In such an arrangement, the walls of the cavity of a resonator may be formed by portions of the support. The walls of the support advantageously form all of the walls of a resonator.
According to another advantageous variant, the resonator is arranged adjacent to the support. In such an arrangement, the walls of the cavity of a resonator may be formed by portions of the support and rim portions.
Such a support is particularly advantageous since it makes it unnecessary to use an additional holder solely for housing the resonator(s). Thus the additional excess weight caused by such holders is avoided. Furthermore, in order to ensure the integration of the resonator(s), it is not necessary to make major modifications either to the rim or to the tire.
According to an advantageous embodiment, the resonator or resonators are Helmholtz resonators. This is a type of resonator which is simple to produce and provides very satisfactory results. This type of resonator is easy and precise to calibrate. It furthermore permits advantageous use without real modification of a safety support of known type, such as described later.
Advantageously, the opening of a Helmholtz-type resonator is of a calibrated diameter and length. The volume V and the calibrated dimensions of the opening are determined so as to attenuate the amplitude or suppress at least one acoustic resonance of the air contained in the cavity C of the tire, corresponding substantially to a given frequency or range of frequencies.
The cavities of Helmholtz resonators are generally of relatively small dimension compared with the wavelength.
According to another advantageous embodiment, the resonator or resonators are quarter-wave resonators.
These are also a type of resonator which is simple to produce and provides very satisfactory results. The dimensioning thereof is particularly simple to effect since it is necessary in particular to provide a length of cavity corresponding substantially to one-quarter of the wavelength on which it is desired to act. Several resonators may have lengths corresponding to one-quarter of several different wavelengths. It furthermore permits advantageous use without any real modification of a safety support of known type, such as described later.
According to another aspect, the invention also relates to a safety support intended to be mounted on a rim of a vehicle wheel within a tire, for supporting the tread of the tire from the inside in the event of loss of inflation pressure. The tire defines with the rim a cavity C, and the support serves to provide at least one of the walls of a resonator suitable for attenuating the amplitude or suppressing a natural resonance of the cavity.
Such a support is particularly advantageous since it makes it unnecessary to use an additional holder solely for housing the resonator(s). Thus the additional excess weight caused by such holders is avoided. Secondly, in order to ensure the integration of the resonator(s), it is not necessary to make major modifications either to the rim or to the tire.
The cavity opening or openings is/are advantageously formed of a tube.
Calibration of such tubes is simpler to effect, more precise and less expensive than the direct calibration of the openings in the walls.
According to an advantageous variant of the invention, the safety support comprises a substantially cylindrical base intended to be fitted around the rim, a substantially cylindrical apex intended to come into contact with the tread in the event of a loss of pressure, and leaving a clearance relative to the latter at nominal pressure, and an annular body connecting the base and the apex. The base, the apex and the annular body define a plurality of cavities c suitable to be connected directly or indirectly to the cavity C by at least one opening. The body may comprise two annular lateral walls connected by a plurality of partitions of substantially axial orientations, such walls and partitions defining with the base and the apex the cavities c. The partitions may be distributed regularly over the circumference.
Advantageously, some of the cavities are interconnected via openings.
According to an advantageous variant, the support is produced by assembling two main elements, the first being formed of a base, an apex and an annular body with a circumferentially continuous annular element, and a plurality of axial partitions; the second being formed of an annular element suitable for closing the cavities c when it is assembled with the base.
According to this particularly advantageous embodiment of the invention, a support of known type is used, comprising a series of circumferentially aligned cavities, but with one side open, to which simply a wall which makes it possible to close these cavities is added, in order to form the cavity of the resonator(s). In order to simplify the arrangement, the openings are provided in the attached wall. This involves a minimal modification of the support, since merely a complementary element is added thereto. It therefore retains substantially the same mass. The costs inherent in such a modification are furthermore minimal.
The present invention also provides for the use of a safety support in a vehicle wheel between the rim and the tire of the wheel, the support being provided for supporting the tread of the tire from the inside in the event of loss of inflation pressure therefrom, in order to form at least a portion of one of the walls of a cavity of a resonator arranged in the wheel and suitable for attenuating a natural resonant frequency of this cavity.